Composite die ring



y 1955 c. H. SCHLECHT rzrm. 2708,512

COMPOSITE DIE RING Filed Sept. 13. 1951 f.\VENTORS RQMM United States Patent O COMPOSITE DIE RING Application September 13, 1951, Serial N0. 246,472 2 Claims. (Cl. 207-17) Bowden, Pa., assignors to Heintz Manufacturing Philadelphia, Pa., a corporation of Penn- This invention relates to improvernents in dies, and more specifically to improved designs of die rings used for the cold extrusion of metals. This invention is particularly useful, but not limited in applicatin, to the manufacture of cartridge shells, shell hodies, and shell casings. lt can also be readily used in the cold extrusion of cylind.rical tubing made of carbon steels of either low, medium, and high carbon content as well as.'alloy steels containing chromium, nickel, manganeseand molybdenurn, and other hard metals having the same properties or characteristics as plain carbon or alloy steels. The invention is particularly suited for use in the extrusion of solid or hollow tubular shapes where fine finish, close tolerances and high physical characteristics are required.

Since the end of World War II, there has been a mounting interest by the metal fabricating industry in this country in the shaping of steel by cold extrusion processes because of the great savings in material as well as in the reduced number of machining operations required to shape the workpieces. In addition, by means of the cold extmsion processes, metal workpieces are obtained that have smooth surfaces with superior stress resistant qualities. Workpieces are also obtained which have significant increases in strength, and this makes it possible to manufacture thinner sections than heretofore feasible.

Metal tubing or shell casings have generally been shaped in the past by conventional methods, such as hot extrusion, forging, drawing and the like. Of these methods, cold drawing of metals has some 'of the features of cold extrusion of metals but the former is to be differentiated from the latter in the kinds of stresses that are developed during the work ing operations. In cold drawing of metals, the metal is formed by the application of tensile stresses whereas in the cold extrusion of metals the workpie'ce is forced to flow as a result of applied compressive stresses.

Extrusion of metals can be accomplished by diirerent 1ypes of processes, two of the most important of which are, i. e., backward extrusion and forward extrusion processes In the first method, hot 01' cold metal is forced to flow in a direction opposite to the travel of the die punch or punch ram. This type of process, basically, is sirnilar to the process of piercing of billet or bar in the first operation of the conventional pierce-and-draw method of manufacturing shell forgings. On the other band, in forward extrusion process, the metal flows in the sarne direction as the die punch, and flows out of the die ahead of the punch at a speed that is gremter than that of the latter.

In cold extrusion or coining of cartridge cases, shell casings, and shell bodies, solid and hollow tubing, and like products, stresses of large magnitude are developed in the conventional die ring due .to the high pressure that must be applied by the die punch to the workpiece in forcing the metal to escape throi1gh the annular orifice between the die ring, which is located on the outside of the piece, and the pilot of the punch, which is located inside of the workpiece.

2,708,512 Patented May 17, 1955 Conventional die rings appear to be subjected to fatigue, and tensile failure. They often fail due to a progressive fracture. This progressive fracture is dependent upon two factors, i. e. the stress level at the die ring surface and the resistance of the metal to the propagation of any cracks that may form in the highly stressed regions of the juncture of the die ring shoulder and the die ring wall proper due to the tremendous pressures Set up by the die punch in forcing the extruded metal through the annular opening between the die ring and the die ilot.

In the conventional die rings, therefore, that were subjected to such trernendous pressures, once a microscopic crack started due to the high stress concentration at the regions of the juncture of the die ring extrusion shoulder and the die ring Wall proper, the crack will propagate with the working of each extruded metal piece. Once a fatigue or tensile crack started at the inner wall it continued to progress toward the outer Wall. Sooner or later the die ring either fractures completely or is discarded prior to the fracture because of this progressive stress damage.

For instance, in a conventional die ring composed' of one integral piece, biaxial stresses on the surface of the die ring and triaxial stresses on the interior of the die ring, composed of tension and compression cornponents, are set up at the regions of the notched juncture of the extrusion shoulder and the die ring proper when a metal workpiece is being extruded. These cornplex stresses are due to the abrupt change in configuration that takes place at the extrusion shoulder. Whenever there is an abrupt change in section, as here, stress concentrations are set up which act as centers or nuclei for cracks and which are more disastrous than the ordinary stresses that would be obtained in an unnotched member.

In addition, prior art die rings cannot be pre-loaded uniformly in a shrink ring assembly due to the varying resistance that is oflered by the ditferences in standard die ring Wall thickness. Pre-loading of die rings is a practice that has been adopted to place the die in compression so that during the extrusion process, the compression stresses must be overcome before the dies are stressed in tension. Therefore, when the factors enumerated above are acting together so as to reinforce each other, high stresses are developed in the die ring when a Shell casing or tu'bular mernber or the like is 'being separation of the metal in a longitudinal direction fromthe extrusion shoulder.

In Order to eliminate these conventional die ring failures, it was originally thought that the proper solution to this problem was to strengthen the die rings by incr easing the wall thickness and overall weights thereof. Die rings designed in this manner also failed during the extrusion process as indicated above. A solution to this important roblem, which forms the basis of this invention, was obtained by forming the die ring assembly in various component parts, which will presently be described.

One of the chief objects of this invention, therefore, is to provide a die ring assembly that can be uniformly preloaded in compression when it is pressed into a shrink ring assembly.

Another object of this invention is to provide a die ring construction that will possess a more uniform eross-section which will minimize stress concentrations and cornbined stresses due to abrupt changes in the inner ring wall configuration.

It is still a further object of this invention to provide a die ring asssembly cornposed of a die ring and an outer new types of die rings that can be successfully employed' toproduce products that have fine surfa'ce finishes, close tolerances, thinner Wall sections and ir'riproved' physical characteristics. This invention is not limited t'o such uses, however.

Another object of this invention is' to provide an improved die ring assernbly Which is simple and economical' to manufacture, accurate' and reliable in operation, and finally which is inexpensive to maintain andreplace.

This invention briefly, therefore, pertains to a composite die ring assembly that has been designed in two parts, such that the bore of an outer ring orsleeve or lirst p'art is' made to such a dimension that'the innen ring or second part is initially pre-loaded before the die ring'assernbly is pressed into'the' shrink ring' assernbly, andwhiCh can lie uniformly preloaded in the shrink ring assembly.

These and other objects of nur invenion as may hereinafter appear will be best understoodfrom a description ofaceompanying drawings, which illustrate a preferred embodirnent thereof, and form a part ofthis application, in which:

Fig. 1 is a sectionalview of a conventional type of forwardextrusion die ring taken through the longitudinal axis thereof;

Fig. 2 is a sectional view of a preferred ernbodirnent f' the invention and taken through the longitudinalaxis of the die ring assernbly;

Fig. 3 is a top plan view of the cnventional die ring construction illustrated in Fig. l With the die pilot and*die punch rernoved;

Fig. 4 is a top planview of the preferred ernbodirnent of the die ring assernbly shown in Fig. 2;

Fig. 5 is a longitudinal sectional view of a conventional die ring showing failure or rupture in the transverse direction; and

Fig. 6 is a longitudinal sectional view of a design of the conventional die ring shown in Fig. 5 and showing failure or rupture thereof in the longitudinal directiom The composite die ring which cornprisesour invention is shown in the drawings in a preferred embodiment, although it is to be understood that departures frorn the construction shown in the drawings can be made Without departing from nur inventive concept;

Referring now to Fig. l, reference numeral 10 refers generally to a conventional type of forged hollow die ring forrnedin a single construction and having integral therewith, at an intermediate inner portionof the ring, an-extrusion shoulder 12. Die ring 10 can oe adapted foreither forward, backward or forward-backward extrusion of metal workpieces. However, it is used primarily for forward extrusion of metal workpieces.

F01 normal worl ing stresses, die rings of this type are satisfactory. However, for stresses in excess of normal, this type of die ring cannot be pre-loaded uniformly in a shrink ring assembly (not shown) dlne to the varying resistance that is ofiered by the diiierences in die ring wall thickness. It will be noted that die ring 10 has a greater Wall thiekness at the bottom portion 14 than at the top Portion 16, with the Wall thiekness increasing from the top portion of the die ring to the bottom portion thereof.

In addition to the disadvantage mentioned above for the conventional die ring, there is another irnportant disadvantage due to the sudden change of shape that oecurs at the extrusion shoulder 12. Here, complex stresses, of large magnitude, are concentrated at the juncture portion 18 located between the extrusion shoulcler portion 12 and the upper portion 16 of die ring l0whenever metal tubing or the like, as shown at 20, is being extruded by means of the die ilot and punch illustrated at 22.

These stress concentrations act as centers o1 nuclei of cracks that continue to propagate progressively either transversely along the junctureportion 18 or longitudinally from the juncture portionl8 at the inner surface 24 of die ring 10. Eventually a failure or rupture of the die ring will occur. Conventional ring dies, sirnilar to the one shownin Fig. l, and which have failed either in the transverse or longitudinal direction because of these high stress concentrations in the vicinity of the upper portion of. the extrusion.shoulder; are illustrated in Figs. 5 and 6, respectively. In order to eliminate these initial centers of failure' and also to' provide a die design by which it is possible t0 make a die assembly which can be more uniformly preloaded when pressed into a shrink ring assernbly, a composite die ring assernbly has been designed.

A preferred ernbodiment of our invention is shown in Fig. 2. The die ring assernbly has been made in two parts, namely, a tubular die ring 26 and an outer ring or sleeve 28, with the configuration of the two combined being the sarne as the c'onventional type die ring shown in Fig'. l. The inner ring 26 has been designed with substantially a eonstant* Wall thickness throughout' its length. The portion 32'ofithe die ring 26 below an extrusion shoulder 30 has been offset from the portion 34 thereabove in order that the die ring will have a uniform Wall thickness throughout for a more uniform preloading cf the die ring.

Die ring 26 has an annular cutout forrned in this lower portion 32 because of the uniform wall thickness thereof. This cutout begins at 36, which would lie substantially in a transverse plane passingthrough the juneture of the extrusion shoulder 30 and the upper ortion 34 oi the die ring, and extends to the lower surface 38 of'the die ring 26. The outer surface 40 of the lower portion 32 is a cylinder of revolution, With its axis coincident With the longitudinal axis 0f the die ring assembly, except that at 42 it is arcuate, the purpose of which is to eliminate abrupt changes in configuration and thns relieve possible regions or nuclei of stress concentrations during'the extruding operation.

The extrusion shoulder 30 is located at an intermediate inner portion ofthe inner ring or sleeve 26. The surface of'the extrusion shoulder forrns an angle that varies according to the die design required.

The outer ring er sleeve 28 is located around the bottom portion 32- of die ring 26, and in the annular cutout forrmd by making the lower portion 32 of the sarne Wall th'ickness a the upper portion 34; The bore of sleeve 28 is made to substantially the Same configuration as surfaces 40 and 42 but of slightly less diameter. Sleeve 28 is shrunk 011 lower portion 32 so that the lauer will be given a greater initial pre-loading than the upper ortion 34. This arrangement allows for the total pre-loading t0 be more uniform after the die assembly is pressed into a shrink ring assembly.

While in the foregoing, specific features have been described in eonnection with nur invention, it is nevertheless to be understood that we do not lirnit ourselves thereto except as the appended claims define the invention in its broa dest sense over the prior art.

Wo claim:

l. A composite die ring for use in a shrink ring assernbly for the cold extrusion of steel and the like, comprising, a tubular die ring for the shaping of a metal Worl(piece to be extruded, said die ring having a substantially constant Wall thickness, said die ring having an extrusion shoulder at an intermediate inner portion there of and forming the outer surface of an orifice through which the metal is extruded over said shoulder during the extruding Operation, said die ring below said extrusion shoulder being offset radially inwardly from the portion of the die ring above said shoulder, and an outer sleeve shrunk on said lower ofiset portion of said die ring, whereby the lower oifset portion of said die ring may be placed under compression so as to receive an initial preloading which when combined with the preloading effected when the composite structure is placed in the shrink ring assembly Will provide substantially uniform preloading for the whole of the composite die ring.

2. A composite die n'ng for use in a shrink ring assembly for the co1d extrusion of steel and the 1ike, comprising, a tubular die ring for the shaping of a metal workpiece to be extruded, said die ring having a sub- Stantially constant wall thickness, said die ring having an extrusion shoulder at an intermediate inner portion thereof and forming the outer surface of an orifice through which the metal is extruded over said shoulder during the extruding operation, said die ring below said extrusion shoulder being oflset radially inwardly from the portion of the die ring above said shoulder, and an outer sleeve shrunk on said lower otfset portion of said die ring, whereby the lower Offset portion of said die ring may be placed under compression so as to receive an initial preloading which when combined With the preloading effected when the composite structure is placed in the shrink ring assembly Will provide substantially uniform preloading for the whole 0f the composite die ring, the outer surfaces of said die ring and said sleeve being a continuation one of the other.

References Cited in the file of this patent UNITED STATES PATENTS 297,551 Agnew Apr. 29, 1884 329,801 Allderdice Nov. 3, 1885 2,245608 Rodgers June 17, 1941 2598975 Coulter Inne 3, 1952 OTHER REFERENCES The Iron Age, pages 90-105, Aug. 4, 1949. 

